Progress in the field of homogeneous catalysis, including homogeneous catalysis of hydrogenation reactions, often involves the development of new ligands and transition metal complexes including these ligands as active pre-catalysts and/or catalysts. The vast majority of ligands used to support transition metal complexes used in homogeneous catalysis are based on P and/or N donor atoms, and an enormous number of such ligands have been designed and synthesized over the past four decades.
It is generally accepted that polydentate chelating ligands bearing NH functionalities (e.g., functional groups) play a crucial role in so-called bifunctional metal-ligand (M/NH) cooperative molecular catalysis, in which a non-innocent ligand is proposed to directly participate in substrate activation via interaction with an N—H group and/or in bond cleavage/formation via N—H proton transfer to or from the substrate. As used herein, the term “non-innocent ligand” is used interchangeably with the term “bifunctional ligand” to refer to a situation in which a ligand interacts with the substrate, including but not limited to hydrogen bonding between the ligand and substrate and direct transfer of atoms and/or electrons between the ligand and substrate or ligand and metal during the chemical reaction. Bifunctional molecular catalysis based on metal-ligand M/NH cooperation was originally developed for asymmetric hydrogenation and transfer hydrogenation of ketones and imines, and is now applicable to a variety of chemical transformations with a wide scope and high practicability. They include practical hydrogenation of carboxylic and carbonic acid derivatives, hydrogenation and electroreduction of CO2, various acceptorless dehydrogenations, asymmetric Michael reaction (addition) of 1,3-dicarbonyl compounds with cyclic enones and nitroalkenes, stereoselective catalytic C—N_ENREF_42 and C—C bond-forming reactions, aerobic oxidative kinetic resolution of racemic secondary alcohols, asymmetric hydration of nitriles, and others.
Given the utility of these catalysts, there is interest in further ligand and catalyst design for the production of commercially important chemicals and intermediates.
α,β-unsaturated alcohols are of great commercial importance, as they are widely used in fragrances, pharmaceutical industries, intermediates in fine chemicals syntheses, etc. Such alcohols may be synthesized using α,β-unsaturated ketones as substrates or starting materials. Non-limiting examples of α,β-unsaturated ketone substrates may have the general form:

The production of α,β-unsaturated alcohols via chemoselective hydrogenation of α,β-unsaturated ketones using molecular hydrogen is quite challenging because of the higher reactivity of the C═C bond compared with that of the C═O group, and hence a tendency to form either the saturated ketone or the fully hydrogenated alcohol. Moreover, the α,β-unsaturated alcohol formed in the hydrogenation reaction may isomerize to the corresponding saturated ketones under commonly used reaction conditions, resulting in lower selectivity for the unsaturated alcohol. Therefore, achieving high C═O/C═C chemoselectivity is a challenge.
C═O/C═C chemoselectivity may be attained via an appropriate catalyst. Examples of such catalysts in the related art are both homogenous and heterogeneous, including a homogenous catalyst having a substrate-to-catalyst ratio (S/C)=5000 (Dowpharma), and a catalyst having an S/C=20,000 (Chirotech Technology Limited). However, these and other prior examples are limited by various drawbacks, including the relatively small S/C ratios. One example of Noyori's catalyst (e.g., a BINAP-Ru complex) showed a higher S/C ratio of 100,000, but required a prolonged reaction time at elevated pressures. (43 hours and 80 atm H2). These conditions limit the use of such catalysts.